Carbocyclines are stable compounds of prostaglandin I.sub.2 and are very useful compounds as an antithrombotic agent. It has recently been found that 9(0)-methano-.DELTA..sup.6 -(9.alpha.)-prostaglandin I.sub.1 (isocarbacyclin) is a compound which displays the strongest anticoagulant action against thrombocyte coagulation among the analogues of carbocycline and is expected to be used as medicine (Ikegami et al., Tetrahedron Lett., 33, 3493 (1983); ibid., 33, 3497, (1983); European Laid-Open Patent Publication No. 0134246).
With regard to the process for producing isocarbocycline, a method in which an epoxide compound expressed by a formula ##STR3## is used as an intermediate (Ikegami et al., Tetrahedron Lett., 33, 3493 (1983)) or a method in which an enolic compound expressed by a formula ##STR4## is used (Ikegami et al., Tetrahedron Lett., 33, 3497 (1983)) has hitherto been known. In these methods, however, the synthetic preparation of the intermediate epoxide compound or enolic compound from the starting material inevitably requires many processes and accordingly these methods of synthesizing isocarbacyclin can hardly be regarded as advantageous ones from the industrial viewpoint.
Apart from these methods, methods have recently been proposed to synthesize isocarbacyclin by use of a bicyclo[3.3.0] octane compound which is expressed by a formula shown below. ##STR5## There are, for instance, such methods as (i) A method comprising introducing an .alpha.-chain to Corey lactone, a starting material, in the Wittig's reaction, establishing the aforementioned bicyclo[3.3.0] octane through an epoxide compound, and further subjecting to the oxidation reaction, Horner-Emmons reaction, and reduction reaction to give isocarbacyclin (Chemistry Letters, 1069 (1984));
(ii) A method comprising introducing two methylene groups to Corey lactone, a starting material, in the Wittig's reaction, establishing a diene compound via diol compound and aldehyde compound, which is then selectively reduced to give the aforementioned bicyclo[3.3.0] octane compound, and following the same procedures as taken in the preceding (i) to obtain isocarbacyclin (Chemistry Letters, 579 (1984)); and PA0 (iii) A method comprising introducing an .alpha.-chain to Corey lactone, a starting material, in the Wittig's reaction, establishing an aldehyde compound, which is then subjected to the intramolecular thermal reaction to establish the aforementioned bicyclo[3.3.0] octane compound, and subjecting this compound to the same procedure as taken in the abovementioned (i) to obtain isocarbacyclin (Tetrahedron Lett., 25, 1067 (1984)).
However, all of these methods have a demerit of being not industrially advantageous since they require multistage processes in obtaining the intermediate bicyclo[3.3.0] octane compound and the overall yield is not so large.